1. Field of the Invention
The invention relates to a vehicle control system that is configured to adapt the behavior characteristics or acceleration and deceleration characteristics (hereinafter, referred to as running characteristics) of a vehicle, such as the power characteristics, steering characteristics and suspension characteristics of a vehicle, to a running environment of the vehicle, the taste and running intention of a driver, or the like, and a vehicle control method that uses the vehicle control system.
2. Description of Related Art
The behavior of a vehicle, such as a vehicle speed and a running direction, varies when a driver performs accelerating or decelerating operation or steering operation. The correlation between an operation amount and a variation in behavior depends on not only an energy efficiency, such as fuel economy, but also characteristics, such as ride comfort, quietness and power performance required of the vehicle. On the other hand, there are various environments in which vehicles run, such as urban areas, expressways, ascending roads and descending roads, and there are various tastes of drivers and various impressions that drivers experience from vehicles. Therefore, even when a vehicle is able to run in line with expectations for a specific running environment and/or a specific driver, but when the running environment or the driver is changed, the vehicle may not run in line with expectations and may give the driver the impression that excessive operation is required or so-called drivability may deteriorate.
Then, in an existing art, there have been suggested various devices that are configured to incorporate driving orientation into behavior control over a vehicle. The device of this type requires no switch operation and allows minute characteristic changes. One example of that device is described in Japanese Patent Application Publication No. 06-249007 (JP-A-06-249007). The device described in JP-A-06-249007 is a driving force control system that uses a neurocomputer. The device is configured to learn the correlation of an acceleration against an accelerator stroke and a vehicle speed as a required acceleration model and then compute a throttle opening degree on the basis of a deviation between the required acceleration model and a second reference acceleration model that incorporates driving orientation and a deviation between the second reference acceleration model and a standard first reference acceleration model.
Note that a situation that the vehicle runs as intended is based on sufficient grip between tires and a road surface. In other words, because the vehicle runs under constraints of tire's grip, the invention described in Japanese Patent Application Publication No. 05-071375 (JP-A-05-071375) is configured to prepare a throttle opening degree map for each of a normal mode and a sporty mode and then correct a target throttle opening degree obtained from the maps on the basis of a road surface friction coefficient (hereinafter, referred to as road surface μ).
The device described in JP-A-06-249007 is configured to incorporate driver's driving orientation into driving force control to increase driving force; whereas, the device described in JP-A-05-071375 is configured to incorporate a road surface μ into throttle opening degree control to relatively decrease driving force (or engine output torque) in order to ensure tire's grip on a road surface. If these devices having opposite control details are merely applied to a vehicle, vehicle running control cannot always be executed sufficiently, so there is room for developing a new technique.